Chromatography Forum

Thanks in advance.

We bought a Therom GC-TSQ MS/MS recently, but kept having trouble with it. For example, we just finished run of about 20 injections, finding the internal standard signal droping linearly from 100% at the begining to 20% at the last sample (peak shape are very good however). We compare the trun files before and after the run, mass signal across the board drops from 40 to 80%. Ion volumn is new, souce was cleaned before the run, sample matrix is not heavy, column aged three month with >200 injections. Anyone here has experinec with this machine? any suggestions to find what the culprit is?

Thanks again

Is this a "within-run" effect only?

Does the response return to "normal" for the start of the next sequence?


or is it a continuous decrease both with and between sequences.


If it is a within-run effect try increasing the time between injections to test see if the effect can be negated or minimized.

Thanks a lot, JGK.

I did have this kind of test, and it appeared to be continuous signal loss between sequences. Once we re-turn the machine (no hardware change), the signal comes back some, and then continue the slide run after run. if there is sth wrong with electric settings, what could be?

One interesting issue that our Thermo contact insists not to use nomial mass, eg. use mass of 77.11 instead of 77, and mass scan width of 0.01amu. This is beyond my minds too, it's a QQQ. Any comments?